GE Industrial Solutions Entellisys 5.0 User Manual - Manual (Page 82)

Single-point functions 82
5
5.2.5 Phase Loss Relay protection
Phase Loss is an optional relay that is part of the voltage relay package. The Entellisys system
performs Phase Loss Relay Protection by comparing the negative-phase sequence voltage to
the nominal 1X value of the system voltage.
For example, in a 120-V wye system, nominal 1X is defined as 120-V phase to neutral. The
negative-phase sequence voltage for the phase-to-phase voltages is used regardless of PT
configuration (i.e., delta or wye). The negative-phase sequence voltage for line-to-line is
calculated as follows:
The parameters in these equations are defined as:
V
N
= negative phase sequence voltage
a = 1∠120 o
a 2 = 1∠240 o
For ABC phase rotation, V
1
= V
ab
, V
2
= V
bc
, V
3
= V
ca
For ACB phase rotation, V
1
= V
ab
, V
2
= V
ca
, V
3
= V
bc
The negative-phase sequence voltages are calculated for the fundamental (60 or 50 Hz)
component only.
The relay can be in three states:
•
Pickup – If the negative-phase sequence voltage is more than the pickup set point, the relay
goes into pickup, and is said to enter Pickup state.
•
Operate – If the relay stays in Pickup state for a specified pickup delay time, the system trips
the appropriate circuit breaker or activates an alarm, and the relay is said to be in Operate
state.
•
Drop out – The relay drops out of pickup when the negative-phase sequence voltage drops
below 97% of the programmed threshold. The relay is said to be in Drop out state.
The phase loss pickup setting can be adjusted from 8% to 50% in increments of 1%. The phase
loss delay setting can be adjusted from 0.5 second to 600 seconds in increments of 0.5 seconds.
Blocking voltage option: An optional blocking voltage is provided and, if enabled, is 5%. The
phase loss relay function is not performed if Blocking Voltage is enabled and the voltage on all
phases is less than the blocking voltage, in which case the system logs an event. If the phase
loss relay goes into pickup, and the voltage subsequently drops below the blocking voltage, the
relay goes out of pickup and the delay is reset. It is possible to suspend the relay through
FlexLogic.
5.2.5.1 Accuracy
Pickup accuracy is ± 4%. Trip time accuracy is ± 0.1 seconds.
( )
3 2
2
1 N
aV V a V
3
1
V
+ + =